Typically shutters comprise a series of horizontal, parallel slats which are pivoted in their retaining frame by pins extending from the rotational center of the ends of the slats and which engage, sometimes loosely, in holes or loops defined by the shutter frame.
Adjustment of the shutter is accomplished by one or more vertical connector strips which is loosely connected to each of the shutter slats by horseshoe-shaped brads or the like. Often the weight of these strips is not taken into account when the shutters are designed, so that when the user tries to set the slats at a certain angle, the weight of the connector strip causes them to fall down into the closed, almost vertical orientation again. Although some friction built into the axle pins of the slats may in the beginning defuse this problem, constant wear will often cause it to reemerge with time.
Even aside from the weight of the adjusting strip, other forces such as wind, impact with wind-blown curtains, and encounter by people in the area will cause the shutter slats to slip to a different angle from that at which they were set.